MOTIONAL NARROWING AND MAGNETOSTRICTIVE BROADENING OF THE MOSSBAUER SPECTRUM DUE TO SUPERPARAMAGNETISM

We present a theory of the effect of superparamagnetic fluctuations on the Mossbauer spectrum through both motional narrowing and magnetostr ictive broadening. The former is the well-known collapse of the hyperf ine splitting due to the rapidly fluctuating hyperfine field. The latt er is a Doppler effect brought about by the fluctuating displacement o f the nucleus. A theory thereof has been previously presented by these authors. However, the two effects were not treated in an integrated f ashion in one comprehensive theory. We do so here.